I think I am finally ready to do a proper installation on our Arctic Fox 30U.However....

In the two years I have been toying with this, technology and the industry have changed. Residential solar has gotten a big boost from various government subsidies, so the choices are much broader now, and prices are coming down.

It is my understanding from the thread listed above that MPPT controllers work well with higher voltage arrays, being able to convert the additional voltage to amps. The last time that I looked at this question, the recommendation was to put a pair of nominal 12v panels in series to get the additional voltage that the MPPT controllers can work with - somewhere between 30 and 50V IIRC.

Typical residential panels are about 31 Voc for a 250 to 280w mono panel, and with these panels now becoming commodity items, prices are getting quite reasonable. 31 V is, IIUC, a good voltage for an MPPT controller to work with - and a single panel should generate that. No need to series a pair of lower voltage panels.

I have room on the roof of my unit for 4 of these panels. 4 x 275 = 1100 watts. Nice!

I realize I can only hope for about half of that with various losses, and the flat non-tilt mounting that I intend to use, but that should still give me over 40 amps on a good day into a battery bank of 6 GC-2's.

Desert_Rat

I believe the only approved RV PV's are the flexible ones, and after thinking I'd go that route I read so many bad things about them that I dropped them from consideration. So, no, your rigid PV's would not be warranted if installed on your RV's roof, but you should also note that they wouldn't be warranted if not installed and maintained by a qualified technician either.

All you can do is buy PV's from highly recommended sources, install them properly, and maintain them so they last. From all I've heard and read, the size PV you've chosen will last just fine on your roof, with the caveat that CanadianSolar is not a very good name. But as long as you properly install them, your roof is no less stable than pole mounted units, of which many PV are installed upon.

Damn near every professional in the field I've talked to about American made Solarworld has either offered or agreed that they're top notch. I'd like to add, however, that I chose not to buy this size panel, and am going with a thinner 26" unit instead because I was afraid that the angling of a 40" width would be troublesome and it would also be subject to more shading.

Solar panels are very robust, and are designed to sit outside in the elements. If it were me, I wouldn't worry about whether or not they were warranted for RV use. Test them before installing them to ensure they work, and if they do, odds are they'll stay working. JMO

I also think Desert Rat is giving you good advice about installing larger than "normal" solar panels. You may have the real estate to mount them, but they may end up being so close to AC shrouds, vents, antennas etc. that they become shaded during the winter months, rendering them useless.

Our coach is 43 feet long, and when I installed our 160 watt mono panels (58" X 26") which are slightly smaller than the same output poly panel, they were as big as I felt I could go without having a shading problem. Even a little shading - just 2 or 3 solar cells - is enough to reduce a panel's output to nothing. FWIW

The larger the panel, the greater the stress will be across it's width. Both from road vibration and from aerodynamic forces by the air getting underneath the panel as you drive down the road.

Standard size house panels have proven to be pretty rugged when they're mounted on the roof of an RV. Time will tell if the larger (wider) panels have the same ruggedness. My guess is not, unless the manufacturer beefed up the thickness and strength of the glass to match the wider widths.

Even a little shading - just 2 or 3 solar cells - is enough to reduce a panel's output to nothing. FWIW

Good to know. This is the reason why I posted this question. Too many variables for the uninitiated to resolve alone. AND, this is one thing I did NOT take into consideration. Better to learn this now!

My main question, however, is: Is this electrically feasible? Residential panels (~31 Voc) charging a 6 GC-2 battery bank through an MPPT controller?

No one commented on that specifically, so I assume that what I have in mind will work -- shading issues aside?

Now, for the shading issue:

In the following, I will use the rated output of the panels for the sake of simplicity, even though we all know that one can expect about 50% of what they are rated for. So, the 'bean counters' can please not split hairs here.

IIUC, you have 6 panels. Basically, three sets of 2 panels in series, correct? If just a few cells of ONE of the panels is shaded, you lose not just the one panel, but the second one in series as well, correct? Shading of one panel costs you 320 watts (2 x 160). However, the two other pairs are not affected (unless they too are shaded). In what I have in mind, I would have 4 inputs, not 3, and I would lose 275 watts if one was shaded, not 320.

I will have to have a close look at my roof in the morning before 9 AM, and again in the late afternoon after 4 PM. IIUC, most of the useful solar day is between those hours (correct me if my assumption is wrong). I can mark out where the panels would go with a felt pen, and then keep an eye on them on the remainder of our trip this year in the morning and evening to see where the shadows fall. If nothing is shaded (or if only one panel is shaded) during peak solar hours, then I suspect that I may be alright. My rig does not have the power needs that yours has, and 1100 watts is WAY more than I need. I just have the space, and the cost is low enough. Even two of those 275 watt panels would be more than double what I have now, and plenty for our needs. I'm just looking for best watts/dollar.

Thanks for the link to SolarWorld. Their 300w panels are fractionally wider, but much longer than the ones that I had linked to just for the sake of reference. I am not stuck on any particular manufacturer at this point -- just looking at the feasibility of using residential panels at all in a mobile setting. Our very heavy and shock absorber equipped Arctic Fox doesn't vibrate a whole lot.

Good to know. This is the reason why I posted this question. Too many variables for the uninitiated to resolve alone. AND, this is one thing I did NOT take into consideration. Better to learn this now!

My main question, however, is: Is this electrically feasible? Residential panels (~31 Voc) charging a 6 GC-2 battery bank through an MPPT controller?

Yes it is feasible. Also you haveing 1100 watts of solar to charge ~660AH of battery is way more than enough.

No one commented on that specifically, so I assume that what I have in mind will work -- shading issues aside?

Now, for the shading issue:

In the following, I will use the rated output of the panels for the sake of simplicity, even though we all know that one can expect about 50% of what they are rated for. So, the 'bean counters' can please not split hairs here.

IIUC, you have 6 panels. Basically, three sets of 2 panels in series, correct? If just a few cells of ONE of the panels is shaded, you lose not just the one panel, but the second one in series as well, correct? Shading of one panel costs you 320 watts (2 x 160). However, the two other pairs are not affected (unless they too are shaded). In what I have in mind, I would have 4 inputs, not 3, and I would lose 275 watts if one was shaded, not 320.

I will have to have a close look at my roof in the morning before 9 AM, and again in the late afternoon after 4 PM. IIUC, most of the useful solar day is between those hours (correct me if my assumption is wrong). I can mark out where the panels would go with a felt pen, and then keep an eye on them on the remainder of our trip this year in the morning and evening to see where the shadows fall. If nothing is shaded (or if only one panel is shaded) during peak solar hours, then I suspect that I may be alright. My rig does not have the power needs that yours has, and 1100 watts is WAY more than I need. I just have the space, and the cost is low enough. Even two of those 275 watt panels would be more than double what I have now, and plenty for our needs. I'm just looking for best watts/dollar.

Yes you are correct. Shade one part, even one module on one panel in a string of several series wired panels, you loose almost all the output of all the series wired panels in that string. That is one of the advantages of wiring in parallel, shade part of one panel you only loose that panel.

Desert_Rat

Thanks for the link to SolarWorld. Their 300w panels are fractionally wider, but much longer than the ones that I had linked to just for the sake of reference. I am not stuck on any particular manufacturer at this point -- just looking at the feasibility of using residential panels at all in a mobile setting. Our very heavy and shock absorber equipped Arctic Fox doesn't vibrate a whole lot.

Thanks.

Frank.

In my case, I found the length of the panels mostly irrelevant. It was their width that mattered because of the center placement of many of our AC's, skylights, etc, along with our RV's being 4x longer than wide. There's also a concern I had about properly angling a 40" PV during periods when sun is low (winter). If 2 40" panels are installed width-wise, can a direct shot to a 30 degree sun altitude be reached by both? I doubt it. I'd think the 1st one would shade the second.

Whatever the case, my point was really about Solarworld. They obviously make many sized panels.

Logged

Desert_Rat

"Good to know. This is the reason why I posted this question. Too many variables for the uninitiated to resolve alone. AND, this is one thing I did NOT take into consideration. Better to learn this now!

My main question, however, is: Is this electrically feasible? Residential panels (~31 Voc) charging a 6 GC-2 battery bank through an MPPT controller?

Yes it is feasible. Also you haveing 1100 watts of solar to charge ~660AH of battery is way more than enough.

No one commented on that specifically, so I assume that what I have in mind will work -- shading issues aside?"

If his PV is planned at 1100w, and battery bank at 12v, doesn't that mean he needs an 100a MPPT? (it does, 91.66 actually). And that's a rather large and expensive unit.

I hesitated on returning to this subject but OP should consider a 24 or 48v battery bank if he's planning on 1100w PV. 12v is a bad idea.

I agree Frank. Such heavy modifications are hard to justify unless there are specific needs. A very effective solar system can be installed on an RV with a 12 volt system. I would also agree that, in most cases, 1100 watts of solar is excessive for a 660 AH battery-bank. It will work, but it'll require a larger controller (more $) and in many cases, power ($) will be wasted, because the batteries won't be able to store all the power the panels are capable of producing.

Most RVs don't consume as much power as ours. Even so, after taking several measurements and a lot of trial and error, we've found that we can camp in southern latitudes, in the winter months with 970 watts of solar (flat-mounted panels) and with an 840 AH battery-bank, without having to run our generator.... as long as we have a mostly sunny day. Our panels now tilt, which has significantly improved their output.

According to Outback, our FM-80 MPPT controller is most efficient with an input voltage of 40 to 44 volts. That equals the output of two of our 160 watt panels wired in series, which is why each two sets of panels are wired in series, with all three sets wired in parallel. Wiring all six panels in parallel would significantly reduce the voltage input to the controller, which would reduce the controller's ability to convert excess voltage to amps - a big benefit of MPPT controllers. It's all about replenishing amps.

No shading whatsoever should be acceptable when installing solar panels on an RV.

1100 watts of solar is excessive for a 660 AH battery-bank. It will work, but it'll require a larger controller (more $) and in many cases, power ($) will be wasted, because the batteries won't be able to store all the power the panels are capable of producing.

Understood. From a dollars and cents perspective, however, if 4 x 275 watt residential panels are cheaper than 6 x 160 watt mobile panels (and so far with just a quick look, that is what I am finding), does efficiency matter? If I end up with more solar capacity than what I need, and therefore some of it is wasted, can I not afford to waste it and still end up being money ahead at the end of the day?

As to the controller, I will need some help here. Again, in a quick lookup, some MPPT controllers are charge current limited. IIUC, a 60 amp current limited controller will not deliver more than 60 amps, and will throttle back the PV array to keep current below that. Wasteful, yes. But if all I want is 60 amps, does it matter?

In addition, while an array may be able to produce 1100 watts under ideal circumstances, how much of that theoretical 91.6 amps am I actually going to see with panels mounted flat on an arched roof in northern lattitudes? At present, I only see a maximum of 8 amps from the single 140 watt factory installed Zamp panel on the roof, and more often it is 6 amps or below. At most I am getting about 60% of rating, but more often 50% or below. If this holds true with 4 x 275w panels, instead of 91.6 amps, I will get, at best, about 55 amps, but more typically, about 46 amps, and that is without calculating any losses in the installation.

So, my question is: Would I need more than a 60 amp controller? (That is the capacity of my converter, BTW).

I was just up on the roof now at 10:30 AM here in Las Vegas, and I see what you mean about the casting of shadows by the stuff installed on the roof. Again, however, if I 'lose' one panel to shading, I only lose 25% of the array, and then only until the shadows move. If the PV array is much bigger than I need, do I care if I lose one panel for an hour or two a day?

Not trying to be difficult. I'm just trying to understand why efficiency trumps price. Please excuse any obvious lack of knowledge and understanding that I am displaying here! I'm just wondering if something can be 'good enough'. 7 liter V-8's were horribly inefficient, but were 'good enough' when gas was cheap. Sunlight is free.

Desert_Rat

I see nothing wrong with your train of thought here. I couldn't do it because the inefficiency would drive me nuts (I'm spaz like that), but if those panels can comfortably fit and you're happy entering your Shelby in the go-cart race, go for it! I mean that sincerely.

It may indeed be cheaper to buy larger panels, with more total output than needed, and accept the fact that a significant amount of that power will be lost due to shading, than to buy smaller "RV" panels that eliminate shading altogether. I don't know... I've never priced panels that I knew would be shaded if I installed them. I'm with Desert Rat though... it would drive me crazy knowing that I was wasting so much power and roof space.

With 1100 watts of partially-shaded panels, at more northern latitudes in the winter, you could probably get by with a 60 amp controller. However, in the summer, in direct sunlight, I'd recommend at least an 80 amp controller. Shading isn't going to be an issue, and controllers emit a fair amount of heat while operating. A 60 amp controller is going to be overloaded in direct sunlight with 1100 watts of solar in the summer.

Our FM-80 (80 amp) is basically just an FM-60 with a self-regulating cooling fan, but that fan kicks on all the time - even in the winter. In the summer, it runs almost non-stop while the panels are charging - and that's with 960 watts of unshaded solar.

I'm with Desert Rat though... it would drive me crazy knowing that I was wasting so much power and roof space.

Hahaha!

Quote

Our FM-80 (80 amp) is basically just an FM-60 with a self-regulating cooling fan, but that fan kicks on all the time - even in the winter. In the summer, it runs almost non-stop while the panels are charging - and that's with 960 watts of unshaded solar.

Interesting... How many amps do you get into your batteries from your array in summer?

Frank.

PS: Where do you mount your controller so that it gets the air it needs, yet you do not hear it in your unit?

It may indeed be cheaper to buy larger panels, with more total output than needed, and accept the fact that a significant amount of that power will be lost due to shading, than to buy smaller "RV" panels that eliminate shading altogether. I don't know... I've never priced panels that I knew would be shaded if I installed them. I'm with Desert Rat though... it would drive me crazy knowing that I was wasting so much power and roof space.

With 1100 watts of partially-shaded panels, at more northern latitudes in the winter, you could probably get by with a 60 amp controller. However, in the summer, in direct sunlight, I'd recommend at least an 80 amp controller. Shading isn't going to be an issue, and controllers emit a fair amount of heat while operating. A 60 amp controller is going to be overloaded in direct sunlight with 1100 watts of solar in the summer.

Our FM-80 (80 amp) is basically just an FM-60 with a self-regulating cooling fan, but that fan kicks on all the time - even in the winter. In the summer, it runs almost non-stop while the panels are charging - and that's with 960 watts of unshaded solar.

I am just throwing this out for consideration.

I have 1500+ watts of solar panels and use 4 charge controllers, ( two 40 amp and two 30 amp controllers).

Blue Sky has a networked IPN system that allows for adding multiple charge controllers up to a couple hundred amps.

I also have three seperate battery banks although the network would support combining them into one large bank.

In the link that I posted I mentioned using the Blue Sky Network configuration. One of the charge controllers acts as the Master Controller and you can add several 40 amp networked MPPT controllers to increase the charging capacity up to well over 200 amps. This system allows for expansion as you add panels or you can set up the full charging capacity up front. One of the benefits is that each charge controller is wired separately and can feed either a single large battery bank or separate battery banks.

Using this network you can maintain a large 12 volt system or several systems and distribute the weight of the batteries rather than having too much tongue weight as mentioned before.

You might want to do some research on the Blue Sky website.

Edit:

I just copied this explanation from the manual.

INSTALLING A MULTI-CONTROLLER SYSTEM USING THE IPN NETWORK The 3000i may also serve as an IPN Network Master controlling up to 7 remote IPN Network compatible Slaves. Any Blue Sky Energy charge controller capable of operating as an IPN Network Slave may be used, and as of this writing include; SB3024i SB3024Di, SB3024iL SB3024DiL, SB2512iX, SB2512iX-HV, and SB1524iX. Another 3000i cannot be used. Controller types and their PV modules may be different. Each controller is installed as a separate standalone charging source connected to the battery and are then networked together. The 3000i serves as the charge control and network communication Master, controls the charging process, and directs the activities of one or more Slaves. No additional communication hardware or software is required to setup or operate the network. A network communication link is established between controllers by daisy chaining a twisted pair cable from the IPN Network terminal block, controller to controller (A-to-A, B-to-B) as shown in Figure 6. Up to 8 IPN based charge controllers can be connected together in a multi-controller system. The 3000i is fixed as device address 0 (zero) and serves as the IPN Network Master. Attached controllers are configured as Slaves set to addresses 1 through 7. If an optional battery temperature sensor is used, only one is required and it must be connected to the 3000i (Master) to be recognized and shared. Optional displays or UCM may connect to any controller on the network.

As I understand this system you could use a 3000I (30 amp mppt) with 7 SB2034iL controllers (40 amp) for a combined charging of 310 amps.

The Charge controllers are not very big. The pictures are in the linked post above, one of a 2034 and the other of a 3000I and a network monitor.

A good analogy for this method of charging is that instead of having a fire hose filling a swimming pool you have several garden hoses. (ie several smaller cables rather than one monster cable).

Another advantage is that a shadow or other problem will only effect the controller output for those panels shaded even though the Master controls all the slave controllers.

Blue Sky has a networked IPN system that allows for adding multiple charge controllers up to a couple hundred amps.

Thanks for that. I noticed that this morning that some companies allow 'stacking' controllers. I'll have a look at that as well, and then look at the price/amp. It appears that I am indeed wading into relatively high power areas for an RV.

I just posted to you and Tom with regard to this issue in the "Bugs" section. When I posted to THAT section from my Android phone using Chrome, it worked fine. Every time I post in THIS section from my Android phone or my Linux Laptop using Chrome, I get the weird font sizes. Perhaps a clue to the problem? In my case, it is repeatable -- every time!

Kevin: How many amps do you get into your batteries from your array in summer?

PS: Where do you mount your controller so that it gets the air it needs, yet you do not hear it in your unit?

ModEdit: Fixed bad text size and quote tags - LS

When our panels were flat-mounted, our Trimetric would indicate that they were putting about 30-32 amps per hour (on average) into our battery bank. Since we started tilting them, we're seeing about 40-42 amps per hour. Those measurements were taken on clear winter days while camping in the So Cal/Arizona deserts, where we often boondock.

On clear summer days, we're seeing 45-48 amps per hour, whether we tilt them or not, but there's really no need to tilt them this far south in the summer.

Our panels were installed with 8 gauge wire from the panels to the junction box, 4 gauge wire from the junction box to the controller and 2 gauge wire from the controller to the batteries. Our controller is installed in a basement compartment, about three feet from the battery-bank.